did you clean the threads in the cylinder before screwing the plugs in? - they get caked in soot and sometimes even cause exhaust leaks as the plugs will torque up but wont seal. You may have had bad spark plugs too if they were following the cylinder misfire.

Does this generation X6 also suffer from the rain tray water drip on the MAF sensor and also cyl5?

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)